1. Field of the Invention
The present invention relates to a planar inverted-F antenna, and especially relates to a compact antenna applied to a wireless communication device, which can be automatically assembled and has an extremely stable structure.
2. Description of Related Art
With the progress of wireless communication technology, more and more electronic devices, such as notebook computers, PDAs or cellular phones, are installed with antennas, so that these electronic devices can be communicated with far-end devices. In these applications, PIFAs are popular as a built-in type or embedded type antenna for mobile communication products because they are light, thin and cost less.
Reference is made to FIG. 1, which shows a perspective view of a conventional PIFA 9. The PIFA 9 has a rectangular-shaped radiation element 91 and a grounding element 92. The grounding element 92 is spaced apart from and parallel to the radiation element 91. The radiation element 91 is extended downwardly with a ground leg 93 and a signal leg 94. The ground leg 93 is electrically connected to the grounding element 92. The signal leg 94 penetrates through the grounding element 92 and is electrically connected to a radio frequency transceiver (not shown) as a signal-feeding leg. When the radiation element 91 senses an external electromagnetic wave, a signal will be transferred to the radio frequency transceiver via the signal leg 94. The radio frequency transceiver enables the radiation element 91 to radiate an electromagnetic wave via the signal leg 94.
The ground leg 93 and the signal leg 94 of the conventional PIFA 9 are located very close together, and consequently the structure is unstable. Two pads 95 and 96 made of insulative material, such as foam or acrylic, are generally disposed between the radiation element 91 and the grounding element 92 for fixing the PIFA 9 and enhancing the structural strength so that it becomes more stable. Because the pads 95 and 96 cannot endure high temperature, the processes of assembling the pads 95 and 96 must take place after the PIFA 9 has been soldered. The pads 95 and 96 cannot be assembled on a PCB automatically and manual assembly is unavoidable. This type of PIFA not only increases the cost of production, but also slows down the manufacturing and assembly process.
In regard to improving the stability and structure of PIFAs, as well as the assembly process, U.S. Pat. No. 6,738,023 ‘MULTIBAND ANTENNA HAVING REVERSE FED PIFA’ was published on May 18, 2005. The multiband antenna is supported by a plastic platform (plastic undercarriage) and is lifted by four metal legs for being soldered onto a PCB directly. The radiation element is placed on the plastic undercarriage, and the plastic platform is fabricated using Micro-Inserting-Molding technology. The legs are made of metal plate by punching, and embedded in the plastic platform during the molding process. This method however, has the disadvantages of complex manufacturing technology and high production costs.
Another prior art is U.S. Pat. No. 6,850,200 ‘COMPACT PIFA ANTENNA FOR AUTOMATED MANUFACTURING’, published on Feb. 1, 2005. The antenna has a radiation element. The radiation element has signal legs on one end thereof. The other end of the radiation element has a non-conductive support structure. The support structure and the signal legs are designed in such a way that they support the radiation element together. This structure improves the stability of the antenna. Furthermore it allows the antenna to be automatically soldered into place. The support structure is made of an insulative material, such as Liquid Crystal Ploymer (LCP), which is able to withstand the heat of solder reflow, whereby it is possible to fix the support structure directly onto a PCB. As such, the antenna can be automatically assembled. Because the support structure's larger size compared to the prior art, the aforesaid conventional antenna has the disadvantage of increasing the area that suffers from a dielectric effect. A further disadvantage is the support structure's complex shape that requires a special material and thereby elevates the costs of production.
In view of the conventional inverted-F antennas, there is a need for improving upon the aforesaid disadvantages.